The invention relates to a method for carrying out hemodynamic measurements on a patient, using a flow-directed balloon catheter, which is connected to a control and pressure-measuring unit and is at least provided with a distal measuring lumen and a balloon-inflating lumen, comprising the steps of inserting the catheter by way of a suitable vein until the distal end is positioned inside the thorax, and of subsequently inflating the balloon and of inserting the catheter further by way of the right atrium and ventricle into the pulmonary artery until the distal end with the balloon in wedge position is stuck in a branch thereof and closes off the latter. By measuring lumen, the opening end of a through tube is meant, which tube is connected at the other end to the control and pressure-measuring unit.
This method and the catheter used for this are known, inter alia, from the article "Hemodynamic Monitoring" by N. Buchbinder and W. Ganz in "Anesthesiology", Aug. 1976, vol 45, no. 2, pages 146-155.
In this known method and catheter, a number of hemodynamic measurements are carried out in order to gain an impression therewith of the functioning of heart and circulation. The pulmonary arterial pressure (PA pressure) and the pulmonary capillary wedge pressure (PCW pressure) play a very important role here. The pulmonary capillary wedge pressure is regarded as being a good measure of the end-diastolic pressure in the left ventricle because there is a continuous head of fluid (blood) between the left atrium and the catheter end in wedge position. As a result the PCW pressure can be designated as the filling pressure in the left atrium. The functioning of the left ventricle as a pump is determined to a considerable extent by the end-diastolic volume in the left ventricle. For a satisfactory approximation of this volume, the end-diastolic pressure in this left ventricle can be used. Catherization of an artery would be necessary to measure this pressure directly. Instead of this, the PCW pressure, which can be assessed by routine measurement with hemodynamic monitors, is used. It is evident that a partial or unsatisfactorily controlled wedge position of the catheter makes the measurement unreliable. A partial wedge position will generally be recognized by the pressure curve shown on a monitor. However, this is not always the case because PCW pressure curves often do not show the "ideal picture" and, because there is great variability in PCW pressure curves.
Additionally, the known method of carrying out hemodynamic measurements has the problem that the PA pressure is measured during introduction of the catheter with the inflated balloon into the pulmonary artery and that the PCW pressure is measured at a subsequent instant when the wedge position of the catheter is reached. It also holds that the PA pressure is measured when the catheter has been brought into position without the balloon being inflated and that the PCW pressure is measured at a subsequent instant, after inflating the balloon. Due to the fact that these curves are recorded only at consecutive instants in this way they can therefore be assessed and evaluated on the monitor exclusively with consideration of the time difference. A further problem which occurs is that a catheter with non-inflated balloon may come in a wedge position which is displaced upwards, which may not be noticed or is not directly noticeable because the PCW pressure curve cannot always satisfactorily be distinguished from the PA pressure curve which is measured first. Such an upward displaced wedge position, which may be caused with a non-inflated balloon by some artefact or other, may have very adverse effects on the blood through-flow in the pulmonary artery of the patient.